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    <title>Chapter 3.  Access Method Operations</title>
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          <th colspan="3" align="center">Chapter 3.  Access Method Operations </th>
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    <div class="chapter" lang="en" xml:lang="en">
      <div class="titlepage">
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          <div>
            <h2 class="title"><a id="am"></a>Chapter 3.  Access Method Operations </h2>
          </div>
        </div>
      </div>
      <div class="toc">
        <p>
          <b>Table of Contents</b>
        </p>
        <dl>
          <dt>
            <span class="sect1">
              <a href="am.html#am_open">Database open</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_opensub.html">Opening multiple databases in a
        single file</a>
            </span>
          </dt>
          <dd>
            <dl>
              <dt>
                <span class="sect2">
                  <a href="am_opensub.html#idm140526457459376">Configuring databases sharing a file</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="am_opensub.html#idm140526460261584">Caching databases sharing a file</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="am_opensub.html#idm140526459479920">Locking in databases based on sharing a file</a>
                </span>
              </dt>
            </dl>
          </dd>
          <dt>
            <span class="sect1">
              <a href="am_partition.html">Partitioning databases</a>
            </span>
          </dt>
          <dd>
            <dl>
              <dt>
                <span class="sect2">
                  <a href="am_partition.html#am_partition_keys">Specifying partition
            keys</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="am_partition.html#am_partition_function">Partitioning
            callback</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="am_partition.html#partition_file_placement">Placing partition
            files</a>
                </span>
              </dt>
            </dl>
          </dd>
          <dt>
            <span class="sect1">
              <a href="am_get.html">Retrieving records</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_put.html">Storing records</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_delete.html">Deleting records</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_stat.html">Database statistics</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_truncate.html">Database truncation</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_upgrade.html">Database upgrade</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_verify.html">Database verification and
        salvage</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_sync.html">Flushing the database cache</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_close.html">Database close</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_second.html">Secondary indexes</a>
            </span>
          </dt>
          <dd>
            <dl>
              <dt>
                <span class="sect2">
                  <a href="am_second.html#idm140526459658848">Error Handling With Secondary Indexes</a>
                </span>
              </dt>
            </dl>
          </dd>
          <dt>
            <span class="sect1">
              <a href="am_foreign.html">Foreign key indexes</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="am_cursor.html">Cursor operations</a>
            </span>
          </dt>
          <dd>
            <dl>
              <dt>
                <span class="sect2">
                  <a href="am_cursor.html#am_curget">Retrieving records with a
        cursor</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="am_cursor.html#am_curput">Storing records with a cursor</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="am_cursor.html#am_curdel">Deleting records with a cursor</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="am_cursor.html#am_curdup">Duplicating a cursor</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="am_cursor.html#am_join">Equality Join</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="am_cursor.html#am_count">Data item count</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="am_cursor.html#am_curclose">Cursor close</a>
                </span>
              </dt>
            </dl>
          </dd>
        </dl>
      </div>
      <p>
        Once a database handle has been created using <a href="../api_reference/C/dbcreate.html" class="olink">db_create()</a>,
        there are several standard access method operations. Each of
        these operations is performed using a method referred to by
        the returned handle. Generally, the database will be opened
        using <a href="../api_reference/C/dbopen.html" class="olink">DB-&gt;open()</a>. If the database is from an old release of
        Berkeley DB, it may need to be upgraded to the current release
        before it is opened using <a href="../api_reference/C/dbupgrade.html" class="olink">DB-&gt;upgrade()</a>.
    </p>
      <p>
        Once a database has been opened, records may be retrieved
        (<a href="../api_reference/C/dbget.html" class="olink">DB-&gt;get()</a>), stored (<a href="../api_reference/C/dbput.html" class="olink">DB-&gt;put()</a>), and deleted (<a href="../api_reference/C/dbdel.html" class="olink">DB-&gt;del()</a>).
    </p>
      <p>
        Additional operations supported by the database handle
        include statistics (<a href="../api_reference/C/dbstat.html" class="olink">DB-&gt;stat()</a>), truncation (<a href="../api_reference/C/dbtruncate.html" class="olink">DB-&gt;truncate()</a>),
        version upgrade (<a href="../api_reference/C/dbupgrade.html" class="olink">DB-&gt;upgrade()</a>), verification and salvage
        (<a href="../api_reference/C/dbverify.html" class="olink">DB-&gt;verify()</a>), flushing to a backing file (<a href="../api_reference/C/dbsync.html" class="olink">DB-&gt;sync()</a>), and
        association of secondary indices (<a href="../api_reference/C/dbassociate.html" class="olink">DB-&gt;associate()</a>). Database
        handles are eventually closed using <a href="../api_reference/C/dbclose.html" class="olink">DB-&gt;close()</a>.
    </p>
      <p>
        For more information on the access method operations
        supported by the database handle, see the <a href="../api_reference/C/db.html#dblist" class="olink">Database and Related
        Methods</a> section in the
        <em class="citetitle">Berkeley DB C API Reference Guide.</em>
    </p>
      <div class="sect1" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title" style="clear: both"><a id="am_open"></a>Database open</h2>
            </div>
          </div>
        </div>
        <p>
        The <a href="../api_reference/C/dbopen.html" class="olink">DB-&gt;open()</a> method opens a database, and takes five
        arguments: 
    </p>
        <div class="variablelist">
          <dl>
            <dt>
              <span class="term">file</span>
            </dt>
            <dd>
                The name of the file to be opened. 
            </dd>
            <dt>
              <span class="term">database</span>
            </dt>
            <dd>
                An optional database name.
            </dd>
            <dt>
              <span class="term">type</span>
            </dt>
            <dd> 
                The type of database to open. This value will
                be one of the five access methods Berkeley DB
                supports: DB_BTREE, DB_HASH, DB_HEAP, DB_QUEUE or
                DB_RECNO, or the special value DB_UNKNOWN, which
                allows you to open an existing file without knowing
                its type.
            </dd>
            <dt>
              <span class="term">mode</span>
            </dt>
            <dd> 
                The permissions to give to any created file.
            </dd>
          </dl>
        </div>
        <p> 
       There are a few flags that you can set to customize open: 
    </p>
        <div class="variablelist">
          <dl>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbopen.html#open_DB_CREATE" class="olink">DB_CREATE</a>
              </span>
            </dt>
            <dd> 
                Create the underlying database and any
                necessary physical files.
            </dd>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbopen.html#open_DB_NOMMAP" class="olink">DB_NOMMAP</a>
              </span>
            </dt>
            <dd>
                Do not map this database into process memory.
            </dd>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbopen.html#dbopen_DB_RDONLY" class="olink">DB_RDONLY</a>
              </span>
            </dt>
            <dd>
                Treat the data base as read-only.
            </dd>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbopen.html#open_DB_THREAD" class="olink">DB_THREAD</a>
              </span>
            </dt>
            <dd>
                The returned handle is free-threaded, that is,
                it can be used simultaneously by multiple threads
                within the process. 
            </dd>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbopen.html#open_DB_TRUNCATE" class="olink">DB_TRUNCATE</a>
              </span>
            </dt>
            <dd>
                Physically truncate the underlying database
                file, discarding all databases it contained.
                Underlying filesystem primitives are used to implement
                this flag. For this reason it is only applicable to
                the physical file and cannot be used to discard
                individual databases from within physical files.
            </dd>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbset_feedback.html#set_feedback_DB_UPGRADE" class="olink">DB_UPGRADE</a>
              </span>
            </dt>
            <dd> 
                Upgrade the database format as necessary.
            </dd>
          </dl>
        </div>
      </div>
    </div>
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